The structures of hydraulic steering clutches and brakes will be explained with reference to FIG. 4. In an actual vehicle, left and right clutches and brakes in pairs are mounted on an axle 9. However, only those on the left side are exemplified in this figure.
During normal advance, the steering clutch 10 is turned on while the brake 11 is turned off so that a power from an input shaft 12 is transmitted to a left output shaft 13 by way of the axle 9 and the left steering clutch 10, and accordingly, a drive sprocket 14 is driven.
In the case of steering, when for example a left steering lever 15 is pulled back from its neutral position, the operation of a hydraulic control valve 17 is started through the intermediary of a link 16, and accordingly, oil from a pump 6 flows into a left clutch piston 7 at a position intermediate of a stroke so that the left steering clutch 10 is turned off.
Thus, the power on the axle is transmitted only to a right output shaft while a left output shaft 13 falls into a free condition, thereby the bulldozer turns moderately to the left.
From this condition, when the left steering lever 15 is pulled further, oil flows also into a left brake cylinder 8 by way of the hydraulic control valve 17 so that the left brake 11 is turned on through the intermediary of a link 18, and accordingly, the left output shaft 13 is made to be stationary, thereby the bulldozer turns sharply to the left.
Incidentally, when a brake pedal 19 is depressed, the left and right brakes are turned on through the intermediary of a link 20, and accordingly, braking is performed in a straight travel condition.
However, such a conventional control device inevitably uses a large size hydraulic control valve which is therefore disposed in an extra space in the vehicle body and which is coupled to the steering lever through a linkage. Accordingly, the structure is complicated, resulting in an increase in manufacturing cost.
Further, in order to enhance the steering ability in a monolever system which is manipulated by a single lever, it is necessary to arrange left and right hydraulic control valves in the vicinity of the steering lever. However, such an arrangement has been difficult for the conventional large size control valve.
The present invention is devised in order to solve the above-mentioned problems inherent to the conventional arrangement, and accordingly, one object of the present invention is to provide a device for controlling hydraulic steering clutches and brakes, which is simple in its structure and which can be manipulated by a monolever.